The Sixth Disctrict court of appeals did address this directly in US v Warshak [0]. What this scare article does a good job of is confusing the reader.
Unopened email left on a 3rd party server for longer than 180 days was considered discarded or abandoned property. Discarded physical property has never retained a reasonable expectation of privacy (for instance, the police are free to dumpster dive once your property is considered discarded). Similarly when you vacate an apartment and leave all your belongings behind, they become the property of the landlord. These are firmly established principles of common law. The waters become more grey when you are not using the 3rd party for communication but for storage, say for emails you have read and leave on the server for 180+ days. [1]
So in this case Congress wanted to establish a new right to privacy that required a warrant on rather vague and nebulous grounds. It was dropped and so the status quo remains.
All the people here complaining apparently have no idea what the law of the land currently is? Email communications residing on a third-party server for less than 180 days that offers services to the public can not be obtained without a warrant. Notification of the issuance of a warrant could be delayed by 90 days. This does not apply to 3rd party services that do not offer services to the public. They can voluntarily disclose content at their whim.
If you believe my understanding to be flawed I welcome the opportunity to be corrected.
[0]: https://www.eff.org/deeplinks/2010/12/breaking-news-eff-vict...
[1]: http://en.wikipedia.org/wiki/Stored_Communications_Act#Overv...